A rollover accident is an extremely hazardous event for a vehicle operator. The danger of rollover accidents is illustrated by data from the Transportation Research Institute at the University of Michigan (UMTRI), which shows that although rollover occurs in less than 5% of accidents involving tractor-semitrailers, these accidents account for 58% of the fatal injuries suffered by truck drivers. Accordingly, in recent years there has been an increased interest in developing systems that can help avoid vehicle rollovers, especially with respect to heavy duty trucks.
Presently known systems for preventing vehicle rollover employ a variety of methods to predict incipient rollover conditions. One known system detects and warns of a rollover condition using sensors to measure the vertical forces acting on each of the vehicle's drive wheels. Another sensor measures the lateral acceleration of the vehicle. Based on these sensor measurements, the system determines when load is transferred laterally between the wheels of an axle. The system also determines the vehicle's center of gravity (CG). This information is used to calculate a lateral load transfer ratio (LTR), which corresponds to the actual roll moment acting on the vehicle. LTR is determined based on the difference between the loads acting on the left and right tires as compared to the sum of the loads acting on the tires. If the load on the left and right tires is equal, then LTR=0 and there is no danger of rollover. As one tire begins to lift off of the ground, as in a rollover condition, the load on the other tire increases until LTR=1. When LTR=1, the wheel on one side of the axle is completely lifted off the ground.
This presently known system also calculates the approximate height of the vehicle's CG, which is also an indicator of a potential rollover. A display provides the vehicle operator with an indication of the LTR and the estimated height of the vehicle's CG to warn the operator of potential rollover conditions. While this system has its advantages, it requires that load sensors be installed at each of the tires for which the forces acting thereon are to be measured. These load sensors would not otherwise be installed on the vehicle and, therefore, represent added cost and complexity for the vehicle.
Another known system detects a rollover event by comparing normal loads estimated for each tire with predetermined threshold values. The normal load on a tire is calculated based on the spring constant k and rolling radius r of the tire. The rolling radius R of each tire can be determined in a number of ways using different variables, including the velocity of the car at the car's CG, sideslip angle, steering angle, length of the wheel track, distance from the axle to the CG, and rotational speed of the tire. However, as most vehicles are not equipped to measure many of these variables, this system also requires that additional sensors be installed on the vehicle.